When using standard size international shipping containers it is important to ensure that as much as possible of the space within the container is filled with the commodity being shipped. This is because, provided a maximum mass limit is not exceeded, the cost of shipping a container is calculated on the basis of volume and not mass.
Palletized loads pose particular problems. The pallet must have a sufficient gap between its upper and lower decks to permit the forks of a forklift truck to pass between them. If the load is in boxes, and the overall height of the pallet and a particular number of layers of boxes exceeds the height of the container by even the smallest amount, then the top layer of boxes must be removed and space is consequently wasted in the top of the container.